Such actuators are very commonly used for producing control movements, for example in valve devices of vehicles or in closing mechanisms of vehicle windows or doors. Depending on its intended purpose the armature can be moved by the coil either in rotation or in translation. To do this the coil is energized with a signal so that it produces a magnetic field, which in turn drives the armature that generates the control movement. The bearing device is designed in accordance with the desired movement direction of the armature and can therefore comprise rotary bearings when the armature is to be rotated by the coil or translation bearings when the armature is to be moved in translation by the coil.
When the coil is energized, as a result of friction the movement sequence of the armature may be irregular and this can cause undesired noise or hysteresis effects. During this the armature alternately sticks, when static friction becomes predominant, and breaks free, whereupon sliding friction predominates. This is also known as the slip-stick effect. In particular, the associated hysteresis effects make it more difficult to control the actuator.
To prevent sticking effects in a valve actuated by an actuator, DE 36 33 312 C1 proposes that in the end positions of the valve a pulsating signal should be fed to a coil of the actuator. In DE 22 46 574, to produce low hysteresis in a valve actuated by an actuator, it is proposed to superimpose a dither- or chopper-signal on a direct-voltage control signal of a coil of the actuator. In both cases the result is that an armature of the actuator is moved continuously relative to the bearing device of the armature, so that sliding friction is predominant and only slight sticking or hysteresis effects, or none at all, can occur.
In practice, however, hysteresis effects that impair the controllability of the actuator still occur. These can be attenuated by increasing the speed of the armature's movement by increasing the frequency of the pulsating signal or the dither- or chopper-signal. However, this is only possible within certain limits since with increasing frequency the speed of the armature decreases again because of its inertia, and consequently, above a limit frequency the advantageous continuous armature movement ceases.